This invention pertains to movable storage systems wherein a series of storage units having shelves or bins, for example, are movable on tracks to create an access aisle between two of the units and to establish the others in close side-by-side relationship to minimize the amount of floor space required for the units. In particular, the invention resides in enhancing the fail-safe features of the electrical control system that governs automatic positioning of the storage units in response to a user request and that monitors safety conditions and the integrity of the system. The control system is an improvement over U.S. Pat. No. 4,437,711 whose entire disclosure is incorporated herein by reference. The patent is owned by the assignee of this application
Typically, the storage units are mounted on track guided wheeled carriages each of which has at least one reversible electric motor propelling it bidirectionally on tracks or rails which may be recessed in the floor. Usually, at least one outermost unit in the series is stationary and other units are controlled to move toward and away from it to form aisles.
The storage unit system described in the cited patent uses a microprocessor based controller to bring about movement of the storage units in the proper directions in response to a user initiated command to open a particular aisle between units. The processor also monitors conditions that have to do with safe operation of the equipment.
In the prior system, the movable storage units are provided on each side with basically conventional safety sweep bars. These bars extend over the length of the sides of the units that face the adjacent units and aisles and they are invariably mounted near the floor so that if an obstruction, such as a person or an article, is encountered by a sweep bar of a moving unit, the sweep bar will open a plurality of series connected switches which will be sensed by the processor. The processor responds by causing the carriage drive motors on all of the storage units to be deactivated until the obstruction lying on the floor is cleared and the system is reset. Safety sweep bars and switches have been used in movable storage unit systems having controllers based on relay logic as well as in microprocessor based controllers such as were pioneered in the cited patent.
Conventional safety sweep switches are suitable for stopping storage unit motion when an inanimate obstruction lying on the floor is encountered. The safety sweep switches will also protect a person against injury by stopping storage unit motion if a control circuit failure or a person who is careless presses a start button to open an aisle at the peril of the preceding user who is presently in an open aisle. The sweep bar on the moving unit will, of course, strike the foot or lower portion of the person in the aisle or the person in the aisle might have the presence of mind to swing his or her foot into a sweep bar to stop the unit before it could press against the upper portion of the person's body. In any case, a person in an aisle is certain to experience substantial consternation during the time which it takes to react by swinging a foot into the safety sweep bar or just having the bar press against the person if the person was close enough to the bar at the instant the units began to move. As applicant has perceived, what these systems need is a safety shutdown switch arrangement which is located on the leading edge on the movable storage units and which is at a higher elevation than the safety sweep bars so that a person would be contacted higher up on the body and so that a person in an aisle could conveniently touch by hand, or by means of an article in the person's hand, a leading edge switch that could be contacted every inch of the way along the length of each side of the storage units.
Another problem in processor based control systems is to assure that failures in the hardware or software used in the system will result in shutting down the system if its self-testing procedure indicates a permanent fault has occurred and not shutting down the system if a hardware or software fault is simulated by high level electronic noise being injected into the system. There should be some means for shutting down the system until it is manually reset for every conceivable failure that is anything but a transient failure.
Another problem in the realm of safety in prior storage unit systems is providing for smooth acceleration and deceleration and thus the right amount of braking of the units following deenergization of the carriage drive motors to bring the units to a stop at such rate as to not cause the carriage wheels to skid or the storage unit to topple as would be the case if braking is too intense. Heretofore, manufacturers would use on all storage systems having the same capacity the same type of brake. Thus, there would be cases where the units were loaded very heavily and other cases where they were loaded lightly. The braking force applied might have been appropriate for the more lightly loaded units but not for the heavier units. No means have been provided heretofore to improve safety by permitting selection of the braking intensity at the installation site commensurate with the load that will be carried by the storage units.